On 08/07/2013 04:47 PM, Linus Torvalds wrote: > On Wed, Aug 7, 2013 at 1:19 PM, Jason Baron <jba...@akamai.com> wrote: >> The whole point of the thread started with wanting to move the default >> 'disabled' branch further out-of-line. > Yeah, but I always disagreed with that. > > Putting the unusual code out-of-line (as in "at the end of the > function") is a good idea, but putting it *far* out of line (as in "in > a different section") likely makes little sense. > > Now, the tracing code is admittedly specialized enough that we could > have some "really cold" attribute and move it to that kind of "even > further away" model, but most of the other uses of the static keys are > not necessarily of the kind where the non-default case is completely > or utterly unlikely - they want to use the static keys not because > some codepath is basically never taken, but because the code-path is > so critical that loading and testing a value from memory is considered > to be excessive for when the feature is turned off (ie scheduler > statistics etc). > > So the code may not even be all that cold - some people may well run > with statistics enabled all the time - it's just that the non-enabled > case really *really* doesn't want to have the overhead of even > bothering to test for this event. > >
ok - I can see 2 variants here as you mentioned: 1) 'Unbiased' - we want to treat both branches equally but don't want the load/test/jmp sequence. For things like the scheduler stats. 2) 'Biased' - where the unlikely path is moved completely out-of-line. And we have a strong 'bias' to optimize the default path. If we can get the completely out-of-line thing working, we could make this distinction. Thanks, -Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
